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United States Patent |
5,536,360
|
Nguyen, ;, , , -->
Nguyen
,   et al.
|
July 16, 1996
|
Method for etching boron nitride
Abstract
The subject invention provides a method of enhancing the etch rate of boron
nitride which comprises doping a layer of boron nitride with an element
from Group IVA of the Periodic Table of the Elements, such as silicon,
carbon, or germanium. The doped boron nitride layer can be wet etched at a
faster rate with hot phosphoric acid than was possible prior to doping the
boron nitride.
Inventors:
|
Nguyen; Son V. (Hopewell Junction, NY);
Dobuzinsky; David M. (Hopewell Junction, NY)
|
Assignee:
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International Business Machines Corporation (Armonk, NY)
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Appl. No.:
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368254 |
Filed:
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January 3, 1995 |
Current U.S. Class: |
216/96; 148/DIG.113; 257/E21.252; 438/517; 438/705; 438/745 |
Intern'l Class: |
H01L 021/311.5 |
Field of Search: |
156/628
148/DIG. 113
|
References Cited
U.S. Patent Documents
3785891 | Jan., 1974 | Vrieze et al. | 156/3.
|
4057895 | Nov., 1977 | Ghezzo | 29/591.
|
4293373 | Oct., 1981 | Greenwood | 156/628.
|
4514251 | Apr., 1985 | van Ommen et al. | 156/628.
|
4875967 | Oct., 1989 | Mishima et al. | 148/DIG.
|
4952446 | Aug., 1990 | Lee et al. | 428/220.
|
5043219 | Aug., 1991 | Yoshida et al. | 148/DIG.
|
5217567 | Jun., 1993 | Cote et al. | 156/657.
|
5227318 | Jul., 1993 | Doll et al. | 148/DIG.
|
Other References
Wolf et al, "Silicon Processing for the VLSI Era"; vol. 1, 1986, pp.
532-534.
Ghandi, "VLSI Fabrication Principles", Silicon and Gallium Arsenide, 1983,
pp. 495-497.
K. Shohno, et al., Surface Passivation CVD-BN Film Applied To Master Slice
p-MOS IC, Extended Abstracts (vol. 79-2) of The Electrochemical Socient,
Abstract No. 413, pp. 1046-1047 (1979).
Masahiko Maeda, et al., A Low-Permittivity Interconnection Using an SiBN
Interlayer, IEEE Transactions on Electron Devices 36: 1610-1614 (1989).
Masahiko Maeda, et al., Low Dielectric Constant Amorphous SiBN Ternary
Films Prepared by Plasma-Enhanced Deposition, Japanese Journal of Applied
Physics 26: 660-665 (1987).
|
Primary Examiner: Hearn; Brian E.
Assistant Examiner: Trinh; Michael
Attorney, Agent or Firm: Heslin & Rothenberg
Parent Case Text
This application is a continuation of application Ser. No. 08/045,570,
filed Apr. 4, 1993, now abandoned.
Claims
What is claimed is:
1. In a method of wet etching boron nitride with phosphoric acid, the
improvement comprising increasing the wet etch rate of said boron nitride
with phosphoric acid by doping said boron nitride with up to 20 percent,
by atomic composition, of an element selected from the group consisting of
silicon, carbon, and germanium.
2. A method for wet etching boron nitride comprising:
(a) doping said boron nitride with up to 20 atom percent of an element
chosen from the group consisting of carbon, silicon and germanium; and
(b) exposing said boron nitride to phosphoric acid.
3. The method of claim 1 wherein said phosphoric acid is at a temperature
of about 165.degree. C.
4. The method of claim 1 wherein said boron nitride is doped with said
element at 2 to 10 percent by atomic composition.
Description
TECHNICAL FIELD
This invention relates to a method for etching boron nitride, and more
particularly to a method of enhancing the etch rate of boron nitride. This
is accomplished by doping the boron nitride with a silicon, carbon, or
germanium, for example and wet etching with phosphoric acid.
BACKGROUND ART
In the field of semiconductor device fabrication, it is common to utilize
insulation layers to separate conductive layers. Silicon nitride layers
applied by plasma-enhanced chemical vapor deposition (PECVD) have been
used as such inter-layer insulation films. These silicon nitride films
have good insulation characteristics as well as high blocking effects
against moisture and alkali metal ions. In addition, silicon nitride
insulation layers exhibit conformal step coverage and high cracking
resistance characteristics. See M. Maeda and T. Makino, Japanese Journal
of Applied Physics 26:660-665 (1987).
However, there are some drawbacks to silicon nitride insulation layers.
Such drawbacks include a relatively high dielectric constant compared with
phosphorous-silicate glass (PSG) and silicon dioxide insulation layers,
leading to relatively large parasitic capacitance and relatively long
propagation delay times between devices. See M. Maeda and T. Makino.
A need for other dielectric or insulation film materials with low
dielectric constants, conformal step coverage characteristics, good
insulation characteristics, and high cracking resistance thus continued to
exist. In response to this need, boron nitride films prepared by
atmospheric chemical vapor deposition (CVD) or PECVD were devised. These
boron nitride films were highly insulating, chemically inert, and
thermally stable. The films also exhibit a low dielectric constant.
However, in order to be useful the boron nitride films must be compatible
with current semiconductor device fabrication processes. Therefore,
suitable etching techniques must be available.
Wet etching processes are common in semiconductor device fabrication
processes. Common wet etchants include hydrofluoric acid (HF), buffered
hydrofluoric acid (BHF), and hot phosphoric acid, for example. These
etchants show little ability to etch boron nitride, and therefore current
fabrication processes are not compatible with the use of boron nitride
insulation layers.
A need thus exists for a method of etching boron nitride using conventional
etchants so that boron nitride can be used in the fabrication of
semiconductor devices. The ability to etch boron nitride will allow the
material to be utilized, and allow one to take advantage of its favorable
insulation layer characteristics.
DISCLOSURE OF THE INVENTION
It is thus an object of the subject invention to provide a method of
etching boron nitride. The method must be compatible with current
semiconductor fabrication processes.
Briefly described, the present invention comprises a method for etching
boron nitride. This is accomplished by doping the layer of boron nitride
with an element selected from Group IVA of the Periodic Table of the
Elements. Group IVA includes silicon, carbon, germanium, tin and lead.
Each of these elements has a structure similar to boron nitride, and the
resulting doped boron nitride is slightly more amorphous while keeping the
same hexagonal bonding structure. After the boron nitride layer is doped
it can be etched using etchants based on phosphoric acid.
The level of doping can be used to control the etch rate of the boron
nitride. Generally, a small amount of the dopant is utilized, ranging up
to about twenty (20) percent without otherwise detracting from the boron
nitride film's physical properties. A range of about two (2) to about ten
(10) percent is preferred.
The doping of the boron nitride thus enhances the ability to etch the boron
nitride using conventional wet etchant techniques. This allows the boron
nitride to be utilized as an insulation layer in semiconductor devices and
allows one to take advantage of the insulation characteristics of the
boron nitride.
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, the broad concept of the subject invention is directed
to a method for etching boron nitride. A layer of boron nitride is doped
with an element selected from Group IVA of the Periodic Table of the
Elements, such as silicon, carbon, or germanium. The doped layer of boron
nitride is then etched, using suitable etchants such as hot phosphoric
acid at about 165.degree. C. Generally, the amount of dopant can range up
to about twenty (20) percent by atomic composition, preferably about two
(2) to about ten (10) percent by atomic composition. These low
concentrations of dopant do not adversely affect the boron nitride
characteristics as an insulation layer. The amount of dopant can be
altered to control the etch rate of the boron nitride.
In one embodiment, PECVD boron nitride films were deposited and doped in a
suitable reactor under the following conditions:
______________________________________
AME5000 Reactor System (Silane Gas Distribution
Blocker)
______________________________________
Pressure: 4.4 Torrs
Temperature: 400.degree. C.
Electrode Spacing:
1.0 cm
Power Density:
2.0 w/cm.sup.2
Gases Flow Rates:
Nitrogen 2,000-20,000
sccm
B.sub.2 H.sub.6 (1% in N.sub.2)
1,000 sccm
NH.sub.3 0-70 sccm
SiH.sub.4 (for Si.sub.x BN)
1-5 sccm
Uniformity (6 Sigma)
<5-10%
Deposition Rate (nm/min)
100 (for BN)
100-140 (for Si.sub.x BN)
Refractive Index 1.75-1.8 (for BN and
Si.sub.x BN)
______________________________________
As indicated, a small amount of silane (SiH.sub.4) is added to form the low
silicon doped (<5 atomic %) boron nitride film. The film has excellent
thickness uniformity and stability toward water vapor. X-ray Photoelectron
Spectroscopic (XPS) analysis shows that films deposited with 5 sccm flow
have less than 5 atomic % silicon content distributed uniformly through
the depth thickness. Films deposited with 1-4 sccm SiH.sub.4 have less
than 5 atomic % silicon doping in the film's bulk. Fourier Transform
Infrared (FTIR) and Transmission Electron Microscopy (TEM) analysis shows
that films deposited with low silicon doping become more amorphous
although they still have the same hexagonal bonding structure. Boron
nitride (BN) and low silicon doped BN (SiBN) films are etched in hot
phosphoric acid (165.degree. C.) and low pressure chemical vapor
deposition (LPCVD) silicon nitride film was used as a reference.
Table 1 shows the etch rate and etch selectivity of boron nitride, low
silicon doped boron nitride, and LPCVD silicon nitride films etched in hot
phosphoric acid. It can be seen that low level silane doping (2-5 sccm
SiH.sub.4, i.e. less than 5 atomic % Si content) enhances the etch rate to
more than three (3) orders of magnitude. The etch rate is also
significantly higher than those of LPCVD silicon nitride, thus making the
use of boron nitride more practical as an insulation layer.
The enhanced etch rate of low silicon doped boron nitride is probably due
to the more amorphous characteristic of low doped Si.sub.x BN compared to
BN. At low doped (<5 atomic %), no significant change in dry etching
behavior is observed and only a small change in the BN properties occur
since the hexagonal bonding still exists.
Low levels of doping by carbon or germanium using CH.sub.4 or GeH.sub.4 as
reactant gases will result in similar etch rate enhancement of the boron
nitride since the doped BN will also become slightly more amorphous while
keeping the same hexagonal bonding structure. Other Group IVA elements can
also be utilized with similar results.
TABLE 1
______________________________________
Etch Rate and Selectivity vs. Silane Flow in Hot
H.sub.3 PO.sub.4 (165.degree. C.)
SiH.sub.4 Flow
Etch Rate
Films (sccm) (nm/hr) Sel. to BN
______________________________________
BN 0 5 --
Si.sub.x BN
1 162 32
Si.sub.x BN
2 5214 1043
Si.sub.x BN
3 6798 1360
Si.sub.x BN
4 7800 1560
Si.sub.x BN
5 10782 2156
LPCVD -- 228 45
Nitride
______________________________________
The chemical composition of the Si.sub.x BN films referred to above were as
follows: (in relative atomic percent)
______________________________________
Silicon
Silane Atomic Nitrogen
Films sccm % Boron %
%
______________________________________
Si.sub.x BN
1 3.6 44.8 50.8
Si.sub.x BN
2 6.7 43.6 49.4
Si.sub.x BN
3 10.1 39.1 49.7
Si.sub.x BN
4 12.5 33.2 53.8
Si.sub.x BN
5 16.0 37.2 46.3
BN 0 0 53.3 46.5
______________________________________
The principles of this invention should also be extendable to other
compounds made up of Group IIIA and Group VA elements. For example, boron
phosphide should exhibit similar insulation and etching characteristics to
boron nitride when doped with a Group IVA element such as silicon.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood by those
skilled in the art that various changes in form and details may be made
therein without departing from the spirit and scope of the invention.
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